Ifconfig eth0 up:
eth0: link up, 100mbps, full-duplex, lpa 0x45E1
This implies that eth0 was down, I think. There should be something in the response from "dmesg" that's relevant to eth0 now.
cat /etc/network/interfaces output:
the loopback network interface
iface lo inet loopback
#The primary network interface
iface eth0 inet dhcp"
Is it working now that you ran "ifconfig eth0 up"? I don't see anything in the interfaces file that would account for the problem you're having. The interfaces entries should have connected you and gotten an ip address from your router assuming the router's not bad. Can you give us the output from "ifconfig" again? This time it should have an entry for eth0, and with any luck, it'll have an address. If not, try running either "dhclient eth0" or "dhcpcd eth0" and then checking ifconfig again. You'll have one of those commands, but probably not both.